The submarine conducted seven patrols and sank 38 ships during the war for a total loss of 97,284 gross register tons (GRT). She operated as part of the Pola Flotilla based in Cattaro. UB-50 surrendered on 16 January 1919 with the remainder of the Pola Flotilla following an order by Admiral Reinhard Scheer to return to port. During her passage through the Straits of Gibraltar, she managed to sink the battleship HMS Britannia. UB-50 was later broken up at Swansea.[3]

UB-50 was ordered by the German Imperial Navy on 20 May 1916. She was built by Blohm & Voss, Hamburg and following just under a year of construction, launched at Hamburg on 6 January 1917. UB-50 was commissioned later that same year under the command of Kapitänleutnant (Kptlt.) Franz Becker. Like all Type UB III submarines, UB-50 carried 10 torpedoes and was armed with an 8.8 cm (3.5 in) deck gun. UB-50 could carry a crew of up to 34 men and had a cruising range of 9,040 nautical miles (16,740 km).[3]UB-50 had a displacement of 516 t (508 long tons; 569 short tons) while surfaced and 651 t (641 long tons; 718 short tons) when submerged. Her engines enabled her to travel at 13.6 knots (25.2 km/h; 15.7 mph) when surfaced and 8 knots (15 km/h; 9.2 mph) when submerged.[3]

Soon after she left Pola, UB-50 encountered the William H. Crawford, a 1,593 GRT American sailing ship. It sank after an attack from the U-boat stopped her.[4] Four days later, UB-50 sighted the 800 GRT British barge R.B.40. UB 50 launched a torpedo which instead hit the British tug towing the ship, the 121 GRTH.s.3. The tug sank, but the barge was not sunk.[5] The following day, UB-50 found two Portuguese sailboats Correiro De Sines and Comizianes Da Graca at 30 GRT and 32 GRT respectively.[6] They were sunk 6 nautical miles (11 km) north of Cape Sines.[7] A day later, she found the Portuguese 233 GRT ship Sado, which she sank about 16 nautical miles (30 km) south of her prey the day before.[8] Four days later, UB-50 finally encountered and sank a merchant, this being the 3,611 GRT British Polar Prince, carrying coal for Malta.[9] Two days later, she sank the Fabian, a 2,246 GRT British steamer going to Liverpool, killing three.[10] Later that day, she sank the Gioffredo Mameli, a 4,124 GRT ton Italian steamer carrying ore.[11] The 2,464 GRT coal carrying Greek steamer Alkyon was attacked two days later by UB-50, sinking close off Oran.[12] The UB 50 followed up with the sinking of the 1,670 GRT Norwegian steamer John Knudsen, killing one.[13] Four days later, the 296 GRT Italian sailboat Ciro was scuttled after being hit by UB-50,[14] the last ship she would sink before returning to base.

SM UB-50 began her second patrol with the sinking of the Marc Fraissinet, a 3,060 GRT French steamer carrying wood, munitions, and hay to Bizerte. It sank 15 nautical miles (28 km; 17 mi) north of Tabarca after being torpedoed by UB-50.[15] Later that day UB 50 encountered the Senegal, an 845 GRT Italian steamer, sinking her off the coast of Algeria with no casualties.[16] Three days after that, the Margram Abbey, a 4,367 GRT British steamer carrying coal, was found and torpedoed by UB-50. It was beached off of the coast of Algeria, but the torpedo damage, which killed two, had wrecked the ship.[17] UB 50 attacked the Antaeus, a 3,061 GRT British steamer, three days later off of Cape Bon. There were no casualties, but the captain was taken prisoner. On the following day, UB 50 torpedoed the Amberton, a 4,556 GRT British steamer, but she was only damaged.[18] Four days later, the submarine found her last target of her second patrol, the 2,774 GRT American steamer Rizal, which sank 9 nautical miles (17 km; 10 mi) from Cape Cavallo.[19]

UB-50 started out her third patrol by finding and sinking the 9 GRT Italian sailboat S. Giuseppe B. off the coast of Africa.[20] She sank the 8,293 GRT British steamer City of Lucknow two days later 50 nautical miles (93 km; 58 mi) northeast of the Cani Rocks.[21] On Christmas Day, 1917, UB-50 sank the Sant’ Antonio, an 843 GRT Italian sailing vessel, by gunfire near Bizerte.[22] On New Year's Day, 1918, the Egyptian Transport, a 4,648 GRT British steamer, was damaged during an attack by UB-50, which killed five men. It was later beached but refloated.[23] Two days later, the Allanton, a 4,253 GRT British steamer carrying coal, was sunk by UB-50,[24] which also sunk the Steelville, a 3,649 GRT British steamer also carrying coal later that day.[25] Four days later, UB-50 torpedoed the Arab, a 4,191 GRT British steamer coal off the coast of Cape Serrat, killing 21.[26]

UB-50 '​s fourth patrol was very successful. In less than a month, she sank six vessels. The first victim was the 2,457 GRT French steamer Saint Jean Ii, which went down 22 March 1918 off of Cap Bon.[27] That same day, UB-50 managed to damage the British steamer Shadwell off of Bizerta.[28] Four days later UB-50 sank the 11,495 GRT Italian steamer Volturno off of Bone (Annaba), Algeria.[29] On 6 April, UB-50 sank the French vessel Madeleine Iii and on 11 April, she sank the Italian sailing ship Carmela G and the British vessel Highland Prince.[30][31]

UB-50 began her fifth war patrol by damaging the 3,296 GRT British steamer Elswick Grange carrying coal off of the coast of Oran, killing one.[32] Two days later, she ran across the 3,152 GRT British steamer Mavisbrook carrying coal. She was torpedoed south east of Cabo de Gata, killing 18.[33] On that same day, she came upon the 168 GRT Danish three-masted iron-hulled schooner Kirstine Jesen, sinking after being fired upon from UB-50's deck gun with no deaths.[34] Two days later, the New Sweden, a 5,319 GRT Swedish steamer, was hit by UB-50 and sank.[35] Two days later, UB-50 found the 180 GRT Spanish steamer Maria Pia, which sank with no casualties.[36] Three days after that, the 117 GRT French sailboat Animal Lafont and 257 GRT Italian sailboat Santa Teresa were torpedoed by the U-boat with no casualties.[37][38]

Shortly before her sixth patrol, Oberleutnant zur SeeHeinrich Kukat took over command from Kptlt. Becker.[39] On her sixth patrol, UB-50 encountered the Imber, a 2,514 GRT British steamer and torpedoed her south of Cape St. Maria di Leuca, though she survived.[40] Three days later, UB-50 sank the War Swallow, a 5,216 GRT British merchant ship carrying coal from the River Tyne to Port Said.[41] Another three days passed before UB-50 found her next target, the Italian steamer Adria 1, a ship carrying cotton from Palermo to Tunis. It sank, but no lives were lost.[42] Two days later, the 5,257 GRT British steamer Upada was torpedoed by UB-50 killing three, but was only damaged.[43]UB-50 sank the Messidor, a 3,883 GRT British coal steamer two days later, sinking the ship and killing one.[44] The following day, she torpedoed the Rutherglen, a 4,214 GRT British steam merchant carrying coal.[45] That was followed by an attack on the Magellan, a 3,642 GRT British steamer on the following day. She sank with one man.[46] The last ship sunk on the patrol was the Antonio S., a 153 GRT Italian sailboat sunk off of the coast of Tunisia.[47]

Britannia sinking in the Atlantic off Cape Trafalgar on 9 November 1918.

On 9 November 1918, two days before the Armistice with Germany, UB-50 sank the British battleship HMS Britannia. The Britannia was on a voyage to Gibraltar when she was torpedoed off Cape Trafalgar.[48] After the initial explosion, the ship began listing ten degrees to port. A few minutes later, another explosion started a fire in a 9.2 in (230 mm)magazine, which resulted in a cordite explosion in the magazine. The Britannia stayed at 10-degrees for 2½ hours before sinking.[1][48] Its 16,350 gross register tons made it the largest ship the U-boat ever sank, and the only one UB-50 would sink during her last patrol.[49]

^ abBurt, p. 253, says that Britannia listed 10 degrees within "minutes" of the first explosion, then held that list for 2½ hours before sinking, while Conway's All the World's Fighting Ships, 1906-1921, p. 9, claims that she stayed afloat for a total of 3½ hours before sinking, making the length of time it took her to sink ambiguous